1. Field of the Invention
This invention pertains to hermetic packages for microelectronic circuits and methods of making them. In particular, it relates to a highly integrated optical modules for high (10 Gbps and higher) data rates.
2. Background of the Invention
Currently, modules for high frequency signals are typically configured as illustrated in FIGS. 1 and 2. FIG. 1 is a perspective view of a conventional module 110 having a xe2x80x9cbutterflyxe2x80x9d configuration. The housing 120 for the module 110 is generally comprised of metal. Holes are drilled through the housing 120 and electrical feedthroughs 130 are inserted in through the holes. The holes are then sealed to isolate the feedthroughs from the housing by firing them at high temperature using a glass material to form a glass-to-metal seal 140 (see FIG. 2). Alternatively, this could be made by high-temperature co-fired ceramic typically consisting of alumina.
As shown in FIG. 2, which is an end-on elevation of the module 110 shown in FIG. 1 taken along line Axe2x80x94A of FIG. 1, a device 150 to be placed inside the module 110 is mounted on a substrate 160 and electrical interconnections 170 are made between the device 150 and substrate 160. The substrate 160 is then positioned within the module 110. Electrical connections 180 interconnect the electrical feedthroughs 130 with the substrate 160 and hence to the device 110. The module 110 is then sealed with a lid 200. Ultimately, the module 110 is placed on and mechanically fastened to a PC board 190 in a known fashion, e.g., through the use of mechanical fasteners through a flange in the module or by cutting a hole in the PC board 190, and placing the module 110 in it. The electrical feedthroughs 130 are then soldered down to the traces on PC board 190. Typically an angled fiber is optically coupled to the photo-detector that is positioned parallel to the angled fiber to receive the optical data stream. Standard transistor out line (TO) packages and dual in line (DIL) packages are also used.
While modules of the configuration shown in FIGS. 1-2 are generally suitable for their intended purpose, they are not without drawbacks. For example, the packages are bulky and cannot be surface mounted. Cavities need to be cut in the PC board to accept the module in order to bring the leads 130 in line with the board so that they can be solder connected. In packages such as DILs the leads must be formed in order to connect to the pc board. The rotational alignment of the angled fiber is cumbersome and increases assembly cost.
Another drawback of a module such as that depicted in FIG. 2 is that a connector such as a K connector is used. This further increases the height of the module because it should be at least as high as the connector.
Another drawback of a module such as that depicted in FIG. 2 is that it may necessitate the use of metal flanges with holes to permit mechanical fastening of the module to the PC board.
Yet another drawback is the very high cost of these packages.
One embodiment of the present invention provides a module including a primary substrate defining a base of the module, wherein the primary substrate is provided with a plurality of vias for electrical connection to a photodetector located within an interior portion of the module; a side wall member joined to the primary substrate to form side walls of the module and to define the interior portion of the module; a secondary substrate positioned within the interior portion of the module, the photodetector being mounted on the secondary substrate; an optical fiber pipe extending into the interior portion of the module from outside the module, the optical fiber pipe being arranged to receive an optical fiber and to position the optical fiber so that light emerging from the optical fiber impinges upon the photodetector; and a lid joined to the side wall member to hermetically enclose the interior portion of the module.
In an embodiment, the primary substrate is comprised of a ceramic material and the vias are comprised of a metallic material, such as a copper-tungsten alloy. In an embodiment, the secondary substrate is comprised of aluminum nitride. In an embodiment, the secondary substrate is placed in a cut-out region of the primary substrate and can carry circuit distribution lines.
In an embodiment, the module also includes an amplifier, such as a trans-impedance amplifier, mounted on the secondary substrate and electrically connected to the photodetector through circuit distribution lines on the secondary substrate. In an embodiment, the photodetector generates a current signal in response to light from the optical fiber impinging on the photodetector, and wherein the circuit distribution lines carry the current to the amplifier.
In an embodiment, the optical fiber pipe extends through the side wall member into the interior portion of the module from outside the module. In an embodiment, the lid comprises a ceramic material, and wherein the optical fiber pipe extends through the lid into the interior portion of the module from outside the module.